As a solid-state image pickup device loaded in an image pickup apparatus such as a copying machine, and having pixel arrays, each of which is composed of an array of pixels, there have been known a CCD solid-state image pickup device and a CMOS solid-state image pickup device.
A CMOS solid-state image pickup device is manufactured on the basis of a CMOS LSI manufacturing process. Accordingly, the CMOS solid-state image pickup device has superior features, as compared with a CCD solid-state image pickup device, specifically, the feature i) it is possible to design a system-on-chip capable of e.g. performing an image processing function, and the feature ii) it is easy to perform high-speed processing. Thus, in recent years, the CMOS solid-state image pickup device has been widely spread.
In recent years, there is a demand for reducing the pixel size in a solid-state image pickup device, as the demands for high-resolution, miniaturization, and low-cost production have increased. In the case where the pixel size is simply reduced, the size of a photoelectric conversion section decreases and the incident light amount decreases, which may lower the sensitivity and degrade the S/N ratio.
As a technology capable of compensating for sensitivity lowering resulting from a reduction in the pixel size, there has been proposed a solid-state image pickup device employing TDI (Time Delay Integration).
For instance, patent literature 1 discloses a technology, wherein TDI is performed with use of a CCD solid-state image pickup device configured in such a manner that pixel arrays and transfer electrodes are alternately arranged in a moving direction (sub-scanning direction). Specifically, a signal charge generated in the first pixel (1, 1) at the first pixel array is transferred to the first pixel (1, 2) at the second pixel array by the first transfer electrode array. Then, the signal charge is transferred to the pixel (1, 3) after summation of the signal charges of the pixel (1, 1) and the pixel (1, 2). Then, the signal charge is transferred to the pixel (1, 4) after summation of the signal charges of the pixel (1, 1) and the pixel (1, 3). Thus, the signal charge generated in the pixel (1, 1) is sequentially transferred while undergoing integration with the signal charges of the pixel (1, 4), the pixel (1, 5), . . . , and the pixel (1, n).
In this configuration, the transfer rate of signal charges between pixel arrays is synchronized with the moving speed of pixel arrays. Accordingly, it is possible to expose each of the pixel arrays at the same subject position. Thus, “n” pixel arrays are sequentially exposed at the same subject position, and signal charges of “n” pixel arrays are integrated, whereby TDI is performed.
Specifically, a photoelectric conversion section of each of the pixels is emptied by completely transferring a signal charge accumulated during an exposure period to a pixel in a next pixel array for time delay integration. Thus, the image pickup device is brought to an exposure start state for a next frame.
As described above, the CCD solid-state image pickup device can easily perform TDI because the CCD solid-state image pickup device can transfer signal charges between pixels.
However, since a CMOS solid-state image pickup element is designed to be driven at a low voltage on the basis of a CMOS LSI manufacturing process, it is difficult to transfer signal charges between pixels.